Cycles of Matter and Human Impact

Cycles of Matter and Human Impact

Middle School

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Learning Objectives

• Learn how matter is recycled in ecosystems through biogeochemical cycles.

• Describe the key processes of the water, carbon, and nitrogen cycles.

• Analyze how human activities can impact these important biogeochemical cycles.

• Define key vocabulary related to the cycling of matter in ecosystems.

Key Vocabulary

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Biogeochemical Cycle

The circulation of essential nutrients through living things and non-living parts of the environment like air.

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Transpiration

The process where plants absorb water and then release it as water vapor from their leaves.

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Combustion

The process of burning fossil fuels, which releases large amounts of carbon dioxide (CO₂) into the atmosphere.

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Nitrogen Fixation

The conversion of nitrogen gas into usable compounds like ammonia by special bacteria or even by lightning.

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Eutrophication

An over-enrichment of water by nutrients like nitrogen, which can cause excessive and harmful algae growth.

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Condensation

The process where water vapor in the air cools down and changes back into liquid water.

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What Are Biogeochemical Cycles?

• Energy flows in one direction, while matter is continuously recycled in an ecosystem.

• ​This exchange of matter through the living and nonliving world is a biogeochemical cycle.

• They involve living organisms (bio), geology (geo), and chemical (chemical) processes.

• These cycles move essential nutrients through the air, water, soil, and all living things.

Multiple Choice

What is the primary role of biogeochemical cycles in an ecosystem?

• To stop the processes of biology, geology, and chemistry

• To prevent matter from moving between organisms

• To create a continuous flow of energy

• To recycle matter through the living and nonliving environment

Multiple Choice

How do biogeochemical cycles support all organisms in an ecosystem?

• By converting all nonliving matter into living organisms

• By stopping the exchange of matter between the living and nonliving environment

• By ensuring that energy flows in only one direction

• By moving essential nutrients through the air, water, soil, and living things

Multiple Choice

What would be the most likely consequence for an ecosystem if the continuous recycling of matter were to stop?

• Organisms would adapt to live without the need for essential nutrients.

• The flow of energy would increase to compensate for the lack of matter.

• The ecosystem would eventually fail because organisms could not get the nutrients they need to survive.

• The ecosystem would find new sources of matter from outside the environment.

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The Water Cycle

• The sun's energy drives the water cycle; the amount of water stays constant.

• Evaporation is when liquid water heats up and rises as water vapor.

• Transpiration is when water vapor is released from the leaves of plants.

• Condensation forms clouds, leading to precipitation like rain, snow, sleet, or hail.

Multiple Choice

What is the primary source of energy that drives the water cycle?

• The movement of wind

• The moon's gravity

• The Earth's core

• The sun

Multiple Choice

How does water vapor in the atmosphere turn into the liquid water that forms clouds?

• It is pushed down by air pressure.

• It is absorbed by dust particles.

• It cools and condenses.

• It heats up and expands.

Multiple Choice

If a large forest is cleared, reducing the amount of transpiration, what is a likely consequence for the local water cycle?

• There will be less water vapor, potentially leading to fewer clouds and less rain.

• The total amount of water on Earth will decrease.

• The rate of condensation will increase, causing heavier fog.

• There will be more water vapor, leading to more clouds and rain.

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Human Impact on the Water Cycle

• Overusing freshwater and groundwater faster than it can be naturally replenished.

• Pollutants contaminate rivers and lakes, which affects the entire water cycle.

• Climate change alters weather, leading to more extreme droughts and floods.

• Diverting rivers for irrigation and building dams changes natural water flow.

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Multiple Choice

Which statement best summarizes the overall effect of the human activities listed?

• They help to clean and purify natural water sources.

• They change or disrupt the natural processes of the water cycle.

• They increase the total amount of fresh water available on Earth.

• They have no significant or long-term effect on the water cycle.

Multiple Choice

How does building a dam or diverting a river for irrigation affect the water cycle?

• It increases the amount of water that evaporates into the atmosphere.

• It changes the natural path and flow of water.

• It removes pollutants from the water.

• It increases the speed of the water cycle.

Multiple Choice

A region is experiencing a severe drought due to climate change. Which additional human action would most likely make the water shortage worse?

• Building a dam to create a water reservoir.

• Limiting the amount of water people can use for gardens.

• Treating polluted lake water to make it clean.

• Increasing the pumping of groundwater for farms and new homes.

The Carbon Cycle

• Photosynthesis removes carbon dioxide (CO₂) from the atmosphere.

• Respiration by organisms releases carbon dioxide (CO₂) into the atmosphere.

• Burning fossil fuels adds large amounts of CO₂ to the air.

Multiple Choice

Which process removes carbon dioxide from the atmosphere?

• Decomposition

• Photosynthesis

• Burning fossil fuels

• Respiration

Multiple Choice

What is the relationship between respiration and photosynthesis in the carbon cycle?

• Both processes remove large amounts of carbon dioxide from the atmosphere.

• Both processes release large amounts of carbon dioxide into the atmosphere.

• Photosynthesis removes carbon dioxide from the atmosphere, while respiration releases it.

• Respiration removes carbon dioxide from the atmosphere, while photosynthesis releases it.

Multiple Choice

What would be the most likely outcome if the global rate of burning fossil fuels increased while the amount of photosynthesis significantly decreased?

• The amount of atmospheric carbon dioxide would increase.

• The amount of oxygen in the atmosphere would increase.

• The amount of atmospheric carbon dioxide would decrease.

• The amount of atmospheric carbon dioxide would stay the same.

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Human Impact on the Carbon Cycle

Burning Fossil Fuels

• Humans add excess carbon dioxide (CO₂) to the atmosphere by burning fossil fuels like coal and oil.

• This combustion process releases carbon that was stored underground for millions of years.

• This is the main way human activities increase the amount of CO₂ in the atmosphere.

Deforestation

• The clearing of forests, or deforestation, reduces the number of trees on Earth.

• Trees absorb CO₂ from the atmosphere for photosynthesis, which helps regulate carbon levels.

• When forests are cleared, less CO₂ is removed from the atmosphere.

Multiple Choice

What is the main way human activities increase the amount of carbon dioxide (CO₂) in the atmosphere?

• By clearing forests for farming

• By using solar and wind power

• By planting new trees in cities

• By burning fossil fuels like coal and oil

Multiple Choice

How does clearing forests contribute to an increase in atmospheric CO₂?

• It increases the amount of fuel available for burning.

• It reduces the number of trees available to absorb CO₂.

• It releases large amounts of stored oxygen.

• It causes soil to release CO₂ into the air.

Multiple Choice

If a community both increases its use of coal for energy and clears a large forest for new construction, what is the most likely combined effect on the atmosphere?

• The level of oxygen in the atmosphere will increase.

• Atmospheric CO₂ levels will significantly increase.

• Atmospheric CO₂ levels will decrease.

• The two actions will cancel each other out, leaving CO₂ levels stable.

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What Is the Nitrogen Cycle?

• The nitrogen cycle moves nitrogen between the atmosphere, soil, organisms, and back again.

• The atmosphere is 78% nitrogen gas (N₂), which most living things cannot use.

• Bacteria are essential for converting nitrogen gas into a usable form for organisms.

• Nitrogen helps build proteins, DNA, and the chlorophyll needed for photosynthesis.

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Multiple Choice

What is the main purpose of the nitrogen cycle?

• To help organisms create their own nitrogen from other elements

• To move nitrogen between the atmosphere, soil, and organisms

• To convert chlorophyll and proteins directly into nitrogen gas

• To increase the amount of nitrogen gas in the atmosphere to 100%

Multiple Choice

Why are bacteria a necessary part of the nitrogen cycle?

• They are the only organisms that use nitrogen to make DNA.

• They turn usable nitrogen back into unusable nitrogen gas.

• They change nitrogen gas into a form that other organisms can use.

• They help plants absorb nitrogen gas directly from the air.

Multiple Choice

If a new disease were to eliminate all nitrogen-converting bacteria from an ecosystem, what would be the most likely long-term consequence?

• The nitrogen cycle would continue without any major changes.

• Organisms would learn to make proteins and DNA without nitrogen.

• The amount of nitrogen gas in the atmosphere would decrease.

• Plants and other organisms would struggle to grow and survive.

Nitrogen Cycle Processes

• Nitrogen gas (N₂) is converted into ammonia (NH₃) by bacteria or lightning.

• Plants absorb nitrogen from the soil to help them grow.

• Nitrogen returns to the atmosphere, completing the cycle.

Multiple Choice

What process is responsible for converting nitrogen gas from the atmosphere into ammonia?

• The action of bacteria or lightning

• The process of plant growth

• Absorption by plant roots

• Its return to the atmosphere

Multiple Choice

What is the primary reason plants need to absorb nitrogen from the soil?

• To provide energy for lightning

• To convert it back into nitrogen gas

• To help them absorb water

• To help them grow

Multiple Choice

What would most likely happen if nitrogen did not return to the atmosphere after being used by plants?

• The amount of nitrogen gas in the atmosphere would slowly decrease.

• Lightning would cease to be a factor in the nitrogen cycle.

• Plants would stop absorbing nitrogen from the soil.

• The amount of ammonia in the soil would permanently increase.

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Human Impact on the Nitrogen Cycle

• Burning fossil fuels releases nitrous oxide (N₂O), which contributes to acid rain.

• Excess nitrogen from fertilizers in agriculture washes into rivers and lakes.

• This overload of nitrogen in water results in massive algae blooms (eutrophication).

• Decomposing algae deplete oxygen in the water, which kills fish and other animals.

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Multiple Choice

Which of the following describes a primary way humans negatively impact the nitrogen cycle?

• Burning fossil fuels and using agricultural fertilizers

• The natural decay of plants and animals

• Planting new forests and creating national parks

• The process of photosynthesis in plants

Multiple Choice

What is the direct relationship between excess nitrogen in lakes and the growth of algae?

• Excess nitrogen removes oxygen from the water, which helps algae grow.

• Excess nitrogen acts as a fertilizer, causing large algae blooms.

• Excess nitrogen has no effect on the growth of algae in lakes.

• Excess nitrogen makes the water too acidic for algae to grow.

Multiple Choice

A large number of dead fish have appeared in a lake located downstream from several large farms. What is the most likely explanation for this event?

• Decomposing algae blooms depleted the oxygen in the water.

• Acid rain from burning fossil fuels directly poisoned the fish.

• The fertilizer runoff made the water too cold for the fish to survive.

• The fish were unable to compete with the algae for sunlight.

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The Phosphorus Cycle and Human Impact

• Phosphorus, a key nutrient, cycles slowly through rocks, soil, and living things.

• Humans mine rocks to create phosphorus-rich fertilizers, disrupting this natural cycle.

• Fertilizer runoff into water can cause massive blooms of algae to grow.

• Decomposing algae use up oxygen, creating dead zones where aquatic animals cannot survive.

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Multiple Choice

What is the primary way humans disrupt the slow, natural cycle of phosphorus?

• By causing the decomposition of algae

• By increasing the amount of oxygen in the soil

• By mining rocks to make phosphorus-rich fertilizers

• By creating habitats for aquatic animals

Multiple Choice

What is the direct relationship between fertilizer runoff and algae in a lake or ocean?

• The fertilizer consumes the algae, reducing their population.

• The algae use the fertilizer to create oxygen for animals.

• The fertilizer and algae have no effect on each other.

• The fertilizer provides nutrients that cause massive algae growth.

Multiple Choice

Which statement best explains how fertilizer use can lead to the creation of 'dead zones' where aquatic animals cannot survive?

• The large algae blooms caused by fertilizer eventually decompose, using up the oxygen in the water.

• The fertilizer runoff makes the water too cloudy for animals to see.

• The fertilizer is directly poisonous to fish and other aquatic animals.

• The algae grow so large that they physically push all of the animals out of the area.

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Common Misconceptions

Misconception	Correction
The amount of water on Earth is always changing.	The total amount of water is constant; it just changes form and location.
Plants can use nitrogen directly from the air.	Nitrogen gas must be ‘fixed’ by bacteria or lightning before plants can use it.
All parts of the biogeochemical cycles happen quickly.	Some cycle components are very long-term, lasting millions of years.

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Summary

• Matter in ecosystems is finite and recycles through biogeochemical cycles.

• The water, carbon, and nitrogen cycles are essential for life on Earth.

• Human activities can add excess nutrients to these cycles, disrupting ecosystem stability.

• This disruption can cause climate change, acid rain, and dead zones.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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